Field of the Invention
The present invention relates to a positive electrode active material used in nonaqueous electrolyte secondary batteries, such as a lithium ion secondary battery.
Description of the Related Art
In recent years, miniaturization and high functionalization of mobile devices such as mobile phones and note-type PCs have been in progress. For the driving power source of those mobile devices, nonaqueous electrolyte secondary batteries, such as lithium ion secondary batteries have been used. The nonaqueous electrolyte secondary batteries have high working voltage and thus have the advantage of higher energy density than other secondary batteries. Due to this advantage, the nonaqueous electrolyte secondary batteries have started being applied in larger machinery such as electric vehicles.
As a positive electrode active material for nonaqueous electrolyte secondary batteries, LiCoO2 (lithium cobalt oxide) has been put in practical use. The nonaqueous electrolyte secondary batteries which use lithium transition metal composite oxides with a layer structure such as LiCoO2 as the positive electrode active materials have average operating voltage of about 3.5 V. Meanwhile, with the use of a lithium transition metal composite oxide which has a spinel structure such as LiMn2O4 (lithium manganate) as a positive electrode active material, a nonaqueous electrolyte secondary battery with an average working voltage of 4V or greater can be obtained. Particularly, when LiNi0.5Mn1.5O4 is used, the average operating voltage can be about 4.5 V.
There has been technology in the lithium transition metal composite oxide which has a spinel structure, for substituting a part of manganese with nickel, other elements, or nickel and other elements according to the purpose.
JP 2009-176583A describes a technology, as the object of achieving higher capacity and improving the cycle characteristics in the secondary batteries, for compensating lithium in LiMn2O4 which has a spinel structure and further for substituting a part of manganese with nickel, boron, iron, or the like.
JP 2013-129589A describes a technology, as the object of improving high rate performance of the secondary batteries, for substituting manganese in LiMn2O4 which has a spinel structure, with nickel and iron or the like.